Several weeks ago, one group of health-conscious Californians took on the Paleo diet and planned to spend nine weeks eating like cave men. That means consuming only animals, vegetables, fruits, nuts, seeds and mushrooms, said Rick Larson, co-owner of CrossFit West Sacramento, the gym running the challenge.

"A lot of people at our gym were getting good workout results, but I knew they weren't supporting it with their diets," Larson said. Because other gyms in the CrossFit family have had success with the Paleo diet, Larson decided to test it at his gym. Fifteen people took the bait.

Like any diet, the hardest thing about the Paleo diet is what you can't eat.

Out is anything that humans began eating after the agriculture and animal husbandry revolutions, meaning no dairy, beans, grains or starches and absolutely nothing processed.

"If you can't eat it raw, then you shouldn't consume it," Larson said. (Although, since our Paleolithic ancestors did have fire, cooking food is permissible.)

The idea of the Paleo diet has been around since the 1980s, but it was popularized in the 2002 book "The Paleo Diet: Lose Weight and Get Healthy by Eating the Food You Were Designed to Eat" by Loren Cordain, a professor at Colorado State University.

Twenty years ago, Cordain read about the diet in a scientific journal and decided to try it.

"For the first time in my life, I started to feel quite healthy, I didn't get any respiratory problems, my arthritis problems went away, and I felt like I gained more muscle mass," he said.

He's been eating like a Neanderthal ever since.

"We are genetically made up with a Stone Age disposition, but we are living in a world of Space Agers," Cordain said.

The Paleo diet even clears up acne, he said.

Larson, the West Sacramento, Calif., gym owner, put his own twist on the Paleo diet. He combined it with the Zone diet, which centers on setting calorie intake parameters but doesn't forbid any kind of food. In Larson's Paleo/Zone diet, the Paleo diet determines what kind of food to eat and the Zone diet guides the quantity.

Following the diet is tough; Larson holds weekly social support sessions with participants.

On a recent Tuesday, Larson told the group they are allowed to have two vices: tea and coffee.

"But not sweetened, and with no dairy," he said.

He points to himself. He's been doing the Paleo/Zone diet for 11 weeks, and his body fat percentage is 2.7, he said.

"Come on! That's how much fat is in my finger," said Santinia Pasquini, 33. Pasquini said she has tried everything from Weight Watchers to diet pills, and in the week she's been doing the Paleo/ Zone diet, she has lost 8 pounds.

It's not even as hard as she thought.

"I thought I was never going to be able to give up Diet Pepsi, but surprisingly, the cravings aren't there," she said.

The Paleo diet

What's in:

Meat, poultry, fish

Fruits

Vegetables

Nuts

Seeds

Mushrooms

Roots

What's out:

Grains

Dairy

Beans and legumes

Refined sugar

Anything processed

A thin slice of dient history

Diet trends come and go, and it can be hard to keep track of them. Some that have evolved a little more recently than cave men:

Zone Diet. Consume different types of calories in balanced proportions. The diet advocates a 40:30:30 ratio of calories obtained daily from carbohydrates, proteins and fats, respectively.

Anyone who knows me also knows that I have a huge sweet tooth. I always have. My friend and fellow graduate student Andrew is equally afflicted, and living in Hershey, Pennsylvania - the "Chocolate Capital of the World" - doesn't help either of us.

It seemed like a good idea at the time: With the incidence of peanut allergy climbing among children, the American Academy of Pediatrics advised parents in 2000 to keep peanuts far away from infants and toddlers who might have a life-threatening reaction to them.

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